title: Delayed appearance of high altitude retinal hemorrhages.
abstract: BACKGROUND
  Retinal hemorrhages have been described as a component of high altitude retinopathy (HAR) in association with altitude illness. In this prospective high altitude study, we aimed to gain new insights into the pathophysiology of HAR and explored whether HAR could be a valid early indicator of altitude illness.
  
  
  RESULTS
  28 mountaineers were randomly assigned to two ascent profiles during a research expedition to Mt. Muztagh Ata (7546 m/24,751 ft). Digital fundus photographs were taken prior to expedition at 490 m (1,607 ft), during expedition at 4497 m (14,750 ft = base camp), 5533 m (18,148 ft), 6265 m (20,549 ft), 6865 m (22,517 ft) and 4.5 months thereafter at 490 m. Number, size and time of occurrence of hemorrhages were recorded. Oxygen saturation (SpO₂) and hematocrit were also assessed. 79% of all climbers exhibited retinal hemorrhages during the expedition. Number and area of retinal bleeding increased moderately to medium altitudes (6265 m). Most retinal hemorrhages were detected after return to base camp from a high altitude. No post-expeditional ophthalmic sequelae were detected. Significant negative (SpO₂ Beta: -0.4, p<0.001) and positive (hematocrit Beta: 0.2, p = 0.002, time at altitude Beta: 0.33, p = 0.003) correlations with hemorrhages were found.
  
  
  CONCLUSIONS
  When closely examined, a very large amount of climbers exhibit retinal hemorrhages during exposure to high altitudes. The incidence of retinal hemorrhages may be greater than previously appreciated as a definite time lag was observed between highest altitude reached and development of retinal bleeding. Retinal hemorrhages should not be considered warning signs of impending severe altitude illness due to their delayed appearance.
authors.affiliation: Department of Ophthalmology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Barthelmes
authors.forename: Martina M
authors.initials: MM
authors.lastname: Bosch
authors.forename: Tobias M
authors.initials: TM
authors.lastname: Merz
authors.forename: Benno L
authors.initials: BL
authors.lastname: Petrig
authors.forename: Frederic
authors.initials: F
authors.lastname: Truffer
authors.forename: Konrad E
authors.initials: KE
authors.lastname: Bloch
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Holmes
authors.forename: Philippe
authors.initials: P
authors.lastname: Cattin
authors.forename: Urs
authors.initials: U
authors.lastname: Hefti
authors.forename: Miriam
authors.initials: M
authors.lastname: Sellner
authors.forename: Florian K P
authors.initials: FK
authors.lastname: Sutter
authors.forename: Marco
authors.initials: M
authors.lastname: Maggiorini
authors.forename: Klara
authors.initials: K
authors.lastname: Landau
mesh_terms: D000328:Adult; D000368:Aged; D000531:Altitude; D000532:Altitude Sickness / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology; D001794:Blood Pressure / Q000502:physiology; D057210:Delayed Diagnosis; D005260:Female; D005654:Fundus Oculi; D006801:Humans; D008297:Male; D008875:Middle Aged; D009051:Mountaineering / Q000502:physiology; D009887:Ophthalmoscopy; D011859:Radiography; D012166:Retinal Hemorrhage / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D013997:Time Factors; D055815:Young Adult